HI,
I'm talking about it doing this for 30 or so seconds when only Safari is open.
Most likely not a lemon but a problem with Safari. Did you install any third party Safari plugins or input managers since you've had your iMac?
If Safari has actually crashed, you can copy/paste a crash report in your reply so we can get an idea of what's causing the problem.
Open a Finder window. From the Menu Bar click Go/Go to Folder
Copy and paste this path into the Finder dialog:
~/Library/Logs/CrashReporter/
Click the Go button.
Finder opens the folder containing the crash log. Look for a the crash file with a date field that looks like the *most recent.* Copy and paste the entire report in your reply.
Carolyn 🙂